Preparing students and families to thrive in the gene age

Sex cells have one set of chromosomes; body cells have two.

Description:

Take a look at human chromosomes.

Transcript:

HI! Let's look at human chromosomes.
This is a photomicrograph of stained human chromosomes from one body cell. How many chromosomes are there?
92. No, count again.
23. No, try again.
These are the broken pieces of one long chromosome. No, Walther Flemming did think that chromosomes exist as one long piece that broke up during
mitosis, but this is not true.
46. That is correct.
Human cells normally have 46 chromosomes; this is the diploid number.
Chromosomes are usually arranged in a karyotype, where homologs are shown side by side. This is useful for identifying some human disorders. In this karyotype, how many pairs of chromosomes are there?
46. No, try again.
23. That is correct.
[HUMAN KARYOTYPE]
Humans have 23 pairs of homologous chromosomes.
How many of these chromosomes will be found in an egg cell?
All 46 chromosomes. No, sex cells have a half set of chromosomes.
23, one from each pair. That is correct.
23, pairs 1-11 and one selected randomly from the remaining pairs. Human sex cells do have 23 chromosomes, but not these 23.
23, 11 random pairs and one extra. Human sex cells do have 23 chromosomes, but not these 23.
None, egg cells don't have chromosomes. No, sex cells do have chromosomes.
Meiosis reduces chromosome number so that sex cells (eggs and sperm) have a half set of chromosomes–one homolog of each pair. This is the haploid number.
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